Internal combustion engines used in automobiles typically operate on fuel-air mixtures, where a fuel injector supplies fuel and a throttle supplies air. On-board computers (also known as Powertrain Control Modules or PCMs) programmed to be responsive to a signal from an accelerator pedal in the automobile, determine the amounts of fuel and air. When a driver wishes to move at a higher speed, he or she presses the accelerator pedal, signaling the computer to supply more fuel, and more air to the engine. The fuel injectors respond by supplying more fuel and the throttle valve responds by opening wider to admit more air to the engine. When the driver wishes to slow down, the driver lifts his or her foot from the accelerator, signaling the fuel injectors to supply less fuel and the throttle to move to a more closed position.
In most internal combustion vehicle engines, a throttle valve controls the engine's idle speed. The throttle valve is typically a metal plate that is positioned on a rotating shaft within the air inlet conduit. The metal plate can be rotated to control the amount of air reaching the cylinders of an internal combustion engine. In many prior art vehicles, the throttle plate's rotational position may be controlled by a linkage connected to the accelerator pedal of the vehicle. The throttle plate may be positioned in a variety of positions, typically within the range of a wide-open, partially open and closed positions. The closed position is sometimes referred to as the “zero position.”
In more modern throttles, an electric motor is utilized to set the throttle plate angle based on signals from an engine controller, such as an electronic Powertrain Control Module (“PCM”). Various inputs into the PCM, such as the accelerator pedal position and the present position of the throttle, are used to calculate the precise throttle plate angle to give the engine the desired performance. Motorized throttles or so-called “electronic throttles,” often integrate with one or more Throttle Position Sensors (“TPS”) to monitor the movement of the throttle plate. The sensors relay the varying movement of the throttle plate to the PCM.
When the PCM calls for more air, the shaft rotates in one direction to open the plate. When less air is needed, the shaft rotates in the opposite direction to close the plate. If the motor fails, the plate must move to a “default” position to maintain some level of engine function. A return spring causes the throttle to close toward the default throttle position when the motor ceases to provide a positioning torque. Default throttle positions are generally described in U.S. Pat. No. 6,129,071, incorporated by reference herein.
During extremely cold weather, there is a possibility of ice forming inside the throttle bore or throttle plate. The ice forms during operation. At engine off, the engine heat is transferred to the throttle, which causes the ice to melt, puddle at the plate edge, and then later re-freeze. The ice can prevent the throttle plate from moving during the next engine start and results in an obstructed (or frozen) throttle condition. This condition will result in degraded (or complete loss of) vehicle function. Vehicle function is affected because, without detection of the frozen throttle condition, normal fault detection and throttle control methods are insufficient to identify the condition and free the throttle plate. The undetected frozen throttle may cause an incorrectly recorded closed throttle position, which occurs when the throttle is incorrectly assumed to be closed. Other faults can also be caused by an undetected frozen throttle. These faults may be detected by the safety monitor system and prevent or limit vehicle operation.
Even if the plate does break free of the ice, an incorrect zero position reference causes higher than intended airflow, which adversely affects engine control. Thus, detection of frozen throttle condition is desired to enable the use of special control methods that can free the throttle plate before other faults are detected that would result in loss of vehicle function. Moreover, once the presence of ice is detected, a method of breaking the ice is desired that will not damage the throttle motor. Furthermore, a method that takes note of the throttle position sensor reading when the throttle is truly closed is desired.